Aptitude - Problems on Trains - Discussion

Nayan correctly said! why they have taken 15 sec for calculating speed of train but not 25 sec? Since distance of signal pole is included in platform, we have to take time taken by train to pass the plateform, and not pole.

Normally we need length of the train gven data has speed and length of the platform and clue is 15 sec because the train has passed the signal post in 15 sec so we have the differnce as 25-15 we get 10 sec.

When we use 25sec as base as nareen and anil said
we should use options which option will verify us anns =10 sec
we can use 25 sec also but with the help of options we can come out .or else we should follow 15 sec as the speed of the train ok.

Hope u got it.

You see they took a signal post because it has a single point kk here we can calculate the speed .

Where as in platform we have two points so we have to add the platform length also to calculate the speed .

So guys we can calulate the speed of the train with one point is very easy So they took 15 sec as the refernce for speed of the train. got it?

If you want to calculate with 25 sec as refernce u should slove by option verification .

150+100=250mts
Total time = signalpost+platform length

25 sec = 15 sec +platform length
platform length =10 sec

so , 250mts/25sec=10mts/sec
So ans is 150 mts.

Is our ans is correct or not let us verify
10mts=1 sec
total length length of plat form time is 10 sec so ,
we have 1 sec=10 mts
10 sec=?
100mts so our ans tallied
We got length of the platform.

(distance or length)/speed=time
in the question both length and speed of train is not given.
So length is x and speed is y.
time given is 15sec.
so x/y=15

and in the next equation we can not write x/y so we interchange it before as y=x/15.
actually it means one and same but to use in equation in right way we have to do it in this way :)

Let length =x
Case 1: speed of train in 15 sec. =x/15
Case 2: since it crossed pole then the total distance = 100+x
Now speed =100+x/25

Now equating both the speeds x/15 = 100+x/25 we get the x value

Thank you pavan.

Please let me know if we can take time as 25-15=10sec.
And solve it as,
Speed=100/10=10sec.

So D/T=S
It means x+100/25=10
x+100=10*25
x=250-100
x=150m.

Let train's length be x meters,

Then, train speed=train length/the time taken to cross the poll.

= x/15.

Train speed=total distance/the time to cross the platform,

x/15 = (x+100)/25.

x = 150.

Let Speed = x m/s.
Distance = 15x m = 15*10 = 150.

Time = 15 secs.
Using d = st,

15x + 100) = 25x.
x = 10.

Therefore - distance = 15x m = 15*10 = 150.

Let trains length is X meter.

When cross the pole the train goes in 1 sec = (100 + X) /25.
When cross the platform the train goes in 1 sec = X/25.

The equation:

(100 + X) /25 = X/25.
X=150.

So the length is 150 m.